• G. Mark Richardson, Ph.D.• Senior Risk Assessment Specialist• Stantec Consulting Limited• Ottawa, ON
THE PERPLEXING DILEMMA OF FINDING THE PERFECT DENTAL RESTORATIVE MATERIAL –
A CHEMICAL RISK ASSESSMENT PERSPECTIVE
What is risk assessment?
–A qualitative or quantitative evaluation of chemical exposures and how those exposures compare to the ‘safe’ dose.
• Risk assessment is never black and white.
– All risks must be weighed relative to the benefits to be gained, and relative to the alternatives that can deliver the same benefits.
Is anything risk-free?• NO!
– Water is toxicCNN.com, Jan 13/07: SACRAMENTO, California (AP) -- A woman who competed in a radio station's contest to see how much water she could drink without going to the bathroom died of water intoxication, the coroner's office said Saturday.
– Oxygen is toxicWhy do you think that it’s important to consume anti-oxidants?
– Staying locked indoors in your home 24/7 is dangerous!
Two locations associated with most injuries and accidents: kitchen and bathroom
Can the (health) benefits outweigh the risks? Can risks outweigh the benefits?
Surgery
Medical/dental X-rays
Immunization
Penicillin
Chemotherapy drugs
Immunosupression drugs
Thallidamide
Humira or Remicade (arthritis drugs) linked to increase risk of cancer
Calcium channel blockers linked to cancer
Hormone replacement therapy (17-ß estradiol) linked to cancer
Amalgam is the most common dental restorative material in the US and Canada
181.1 million Americans of all ages carry a grand total of 3.68 billion restored tooth surfaces, which equates to 1.46 billion restored teeth. The vast majority of these are restored with dental amalgam.
A molar has 5 surfaces (lingual, buccal, mesial, distal, occlusal)Other teeth have 4 surfaces (no occlusal or chewing surface)
Numerous studies have demonstrated that Hg exposure increases with increasing amalgam load:
In exhaled and intra-oral air of persons with amalgam fillings
In saliva of persons with amalgam fillings
In blood of persons with amalgam fillings
In urine of persons with amalgam fillings
In feces of persons with amalgam fillings
In various organs and tissues of persons with amalgam fillings, including: kidney, pituitary gland, liver, and brain or parts thereof
In amniotic fluid, cord blood, placenta, and various foetal tissues in association with maternal amalgam load, including: liver, kidney and brain
In colostrum and breast milk in association with maternal amalgam load
Hg exposure in dental patients
From Dunn et al. 2008. NE Children’s Amalgam Trial
Number of amalgam surfaces
Large fillings cause more exposure than small fillings, but most researchers do not measure the size of the filling, just how many.
Dental amalgam 50% Hg0 by weight
Most significant single source of exposure to Hg for amalgam-bearing population (acknowledged by Health Canada)
The only material that is a recognized hazardous material before entering the mouth, a hazardous waste when removed from the mouth, but deemed ‘safe’ when in the mouth
Health Canada recommends avoiding placement in children, pregnant women, persons with other metallic dental work (such as braces), persons with kidney ailments
Now banned in Sweden and Norway.
Regulatory Hazard Rankings for Hg
EPA list of toxic pollutants (1978)
EPA list of Priority Pollutants (1982)
#3 on CERCLA Priority List of Hazardous Substances
Canadian List of Toxic Substances since 1988
Society of Toxicology (2009) – Hg only surpassed by concern for
tobacco use (smoking, chewing, second-hand smoke)
Superfund: Elemental Hg in 48.7% of 1,467 NPL sites (ATSDR
1999) (NPL = 1,689 sites in 2007)
Hazardous waste
UNEP international phase out initiative
Established RELs for Hg0
Agency orAuthor
Year Terminology REL(µg Hg0/m3)
REL-equivalent absorbed dose(µg Hg/kg-day)1
California EPA 2008 Chronic reference air concentration (RfC)
0.03 0.005
Richardson et al 2009 Chronic referenceexposure level (REL)
0.06 0.01
Lettmeier et al 2010 Chronic reference airconcentration (RfC)
0.07 0.011
US ATSDR 1999 Chronic minimal risklevel (MRL)
0.2 0.032
US EPA 1990 Chronic reference airconcentration (RfC)
0.3 0.048
1. REL-equivalent dose calculated as per US EPA (2004)
2. The USEPA REL for methyl Hg = 0.1 µg/kg-day (2 times greater than EPA REL for Hg0)3. The HC REL for methyl Hg = 0.2 µg/kg-day (20 times greater than HC REL for Hg0)
CalEPA
Richardson et al. & Lettmeier et al.
US ATSDR
US EPA
100%
97%
76%
59%
Total N = 82.5 million adults (21-60y)
Frequency Histogram - Adults
Exposure to Hg0: Dose versus REL
CalEPA
Richardson et al. & Lettmeier et al.
US ATSDR
US EPA
100%
100%
49%
29%
Total N = 7.7 million children (5-13y)
Frequency Histogram - Children
Results
TODDLERS CHILDREN TEENS ADULTS SENIORS Total pop > REL
Total pop with fillings 379,004 7,714,637 11,289,979 82,524,655 20,403,213 122,311,488
% > CalEPA REL 100 100 100 100 100 122,311,488
% > Richardson et al REL 100 100 97.2 98.0 97.9 119,908,745
% > Lettmeier et al REL 100 99.7 95.3 96.2 96.0 117,784,675
% > US ATSDR REL 60.0 48.8 49.4 75.7 77.3 87,852,641
% > US EPA REL 45.2 29.2 30.8 59.0 61.9 67,220,662
‘Safe’ Number of Amalgam-Filled Surfaces(N ≤ REL)
Age group REL sourceREL
(µg Hg/m3)REL-associateddose (ug/kg-d)
No. Surfaces≤ REL dose
Toddlers,children &young teens
California EPA (2008) 0.03 0.005 0.6
Richardson et al (2009) 0.06 0.01 1.3
Lettmeier et al (2010) 0.07 0.011 1.4
US ATSDR (1999) 0.2 0.032 4
USEPA (1990) 0.3 0.048 6
Older teens,adults &seniors
California EPA (2008) 0.03 0.005 0.8
Richardson et al (2009) 0.06 0.01 1.7
Lettmeier et al (2010) 0.07 0.011 1.8
USATSDR (1999) 0.2 0.032 5.3
USEPA (1990) 0.3 0.048 8
Published Estimates of Hg Exposure in Adults With Dental Amalgam
0 5 10 15
3.4; 0.15 - 11.6
Estimated adult Hg dose from amalgam (mg/day)
Richardson&Allan (1996) ARichardson&Allan (1996) B 3.7; 0.24 -11.5
1 - 12. 5
3 - 17
4.5; 0.3 - 13.9
CCEHRP (1993)
Halbach (1995) A
WHO (1991)
Halbach (1995) B 3.4; 0.1 - 11.8
Weiner & Nylander (1995) 9; 4 - 19
2.3; 0.5 - 4Olsson & Bergman, 1992
Vimy & Lorscheider , 1990Berglund , 1990 1.7; 0.4-4.4
Aronsson et al., 1989
Mackert , 1987 1.24; 0.51-1.83
7.7; 2.5 - 17.5Clarkson et al., 1988
Patterson et al., 1985
10 ; 4.0 – 14.7
Mackert , 1991 1.2
Mackert & Berglund , 1997 1 to 3
USEPA RfC for Hg
CalEPA RfC
for H
g
Mean: 4.9 – 10.1; Range: 0.44 – 45.6
Richardson et al (2011)
3.8 µg/day
0.38 µg/day
9.1 ; 1.5 – 21.5
6.5 ; 0 - 27
WHO (2003) 1 – 21.6
Recent interesting facts about amalgam use in Canada:
1. Canadian Mercury Imports for Use in Dentistry Appear to be Rising
1 2 30
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
YEAR
QUA
NTI
TY IM
PORT
ED (k
g)
1994 1999 2008
2130 kg
1642 kg
4700 kg
Recent interesting facts about amalgam use in Canada:
2. >985,000 amalgam fillings were placed into Canadian children’s baby teeth since 1996 (Statistics Canada, 2007 Canadian Health Measures Survey).
In 1996, Health Canada recommended that “non-mercury filling materials should be considered for restoring the primary teeth of children”.
Dental amalgam – Risks to Dentists - 1
• Sources of Hg vapour exposure in dentists– Vapour in office air
Hg leakage from stored capsulesHg leakage during triturationHg leakage by inappropriate disposal of spent capsules in operatory trashHg emission from contaminated amalgamatorsHg emission from heat sterilization of contaminated dental instrumentsHg emission from office dust (amalgam particles) on sills and other surfacesHg emission from chair-side saliva extractors/aspirators
– Vapour in dentist/patient breathing zone during removal of old amalgam fillings
– Amalgam particles in dentist/patient breathing zone during removal of old amalgam fillings
Dental amalgam – Risks to Dentists – 2Typical Hg vapour levels in dental ‘environments’
100
50
10
2500Breathing zone during removal - dry drilling
Breathing zoneduring removal - spray + aspiration
Average dental office air Hg level
Hg
air
co
nce
ntr
atio
n (
µg
/m3 )
25Occupational TLV = 25 µg/m3
Dental Amalgam – Risks to Dentists - 3
Cloud of amalgamparticulate
Equivalent Hg concentration:~85,000 µg/m3 during a
removal procedure
3 µm
What masks are designed to stop?> 3 µm
Dental amalgam – Risks to Dentists – 4
Are standard hygienic masks any help against particulate?
Average amalgam particle size = 2 µm
> 65% of amalgam particles < 1 µm
Is no dental health care preferable to or safer than no dental amalgam?
Risks to patients from composite resin materials• Bisphenol-a observed in saliva following placement of composite resin
fillings
• Bisphenol-a is an endocrine disruptor• mimics 17β-estradiol (but to what extent?)
Uncertainties with data and studies linking BPA to risk
BPA is between 1,000 times and 10,000 times less potent as an endocrine disruptor than 17β-estradiol
17β-estradiol is prescribed in Canada (and elsewhere) for hormone replacement therapy, birth control, treatment of severe acne, and local (topical) treatment of symptoms of menopause
Sources and Levels of Bisphenol-a Exposure(Richardson et al., 1997; 1999)
1.0 E-070.02
0.180.18
0.38
25.0 HC REL
50.0 US EPA REL
AIR
BEVERAGE
DENTALFOOD
TOTAL
Source
0.0
0.2
0.4
0.6
0.8
1.0
Est
imat
ed d
aily
dos
e (u
g/kg
-day
)
* * Assumes that all fillings are composite resin
Potential risks to dentists from composite resin materials
• Inhalation of plastic particles when old resin fillings drilled to remove– Not an issue if repair added on top of old resin filling
• Occupational dermatitis due to exposure to methylmethacrylate (component of BIS-GMA)
Is composite resin preferable to or superior to or safer than amalgam as a dental restorative material?
Risks posed by gold restorations• Gold is the noblest of metals
– i.e., supposedly the least reactive
• However, the reported rate of allergy to gold is similar to that reported for mercury– Gold = 20% to 45% depending on degree of sensitization– Mercury = 5% to 45% depending on degree of sensitization
• The levels of gold, platinum and palladium in blood or urine correlate with the number of tooth surfaces restored with gold alloys– Are there risks posed to dental patients by gold restorations?– Are there risks posed to dentists by working gold
restorations?
Is gold preferable to or superior to or safer than composite resin and amalgam as a dental restorative material?
Other dental materials needing assessment: Gold alloys
Au, Ag, Cu, Pd, Zn, Pt, In
Ceramics U, Cu, Pb, Zn
Glass ionomers and resin-modified ionomers Floride, Al, Sr, Zn, HEMA, polyacrylic acid, TEGDMA
Pit and fissure sealants used to prevent cavities in children Bis-GMA, TEGDMA, UDMA, HEMA, BPA, methacrylic acid, formaldehyde, SiO2,
Ti02
Base metal alloys used for bridges and partial dentures Ni, Cr, Co, Mo, Ti, W
Gallium alloys Ga, Ag, Sn, Cu, Pd, Zn, Pt
Take home messages Mercury exposure from dental amalgam is significant.
To reduce Hg exposure, reduce the number of amalgam fillings.
Even one amalgam filling will exceed the most stringent safe exposure limit for Hg vapour. For an average of 8 amalgam-filled teeth, Hg exposure is 20 Xs greater than the CalEPA REL.
Composite resin materials are safer; exposures more than 50 times lower than RELs
As a dental patient, exposure to Hg vapour and particulate occurs during removal of amalgam fillings. Does your dentist take measures to protect you from that exposure?
If you are a dentist and are removing old amalgam fillings, take suitable health and safety precautions to protect yourself and your staff from exposure to Hg vapour and particulate.
Dentists need more than a simple hygienic mask to protect themselves from those exposures. Vapour and particles will pass through a simple hygienic mask.
There is still more work to be done to assess risks posed by dental materials.
Some published reports & articles on dental materials by GM Richardson
• Mercury exposure and risks from dental amalgam in the US population, post-2000. Science of the Total Environment, 409: 4257-4268. 2011.
• Mercury Exposure and Risks from Dental Amalgam, Part 1: Updating Exposure, Re-examining Reference Exposure Levels, and Critically Evaluating Recent Studies. Report distributed by the US FDA to members of the FDA Expert Panel for Review of Dental Amalgam. Dated November 8, 2010.
• Mercury Exposure and Risks from Dental Amalgam, Part 2: Cumulative Risk Assessment and Joint Toxicity: Mercury Vapour, Methyl Mercury and Lead. Report distributed by the US FDA to members of the FDA Expert Panel for Review of Dental Amalgam. Dated November 11, 2010.
• Inhalation of mercury-contaminated particulate matter by dentists: an overlooked occupational risk. Human and Ecological Risk Assessment, 9(6): 1519-1531. 2003
• Waste mercury in dentistry: the need for management. Environmental Health Review, 47(2): 33-39. 2003
• Mercury Exposure From Dental Amalgam: Re-evaluation of the Richardson Model, Standardization by Body Surface Area, and Consideration of Recent Occupational Studies. In: Amalgam and Health - New Perspectives on Risks, Report 99:1, FRN, Sweden. 1999
• Dental Amalgam and Mercury Exposure: Potential Patient Risks and the Basis for Restrictions on Use. In: Amalgam and Health - New Perspectives on Risks, Report 99:1, FRN, Sweden. 1999
• Preliminary estimates of adult exposure to bisphenol-a from dental materials, food and ambient air. In: Henshel et al. (eds). Environmental Toxicology and Risk Assessment: Standardization of Biomarkers for Endocrine Disruption and Environmental Assessment. Eighth Volume, ASTM STP 1364, ASTM. 1999.
• An assessment of adult exposure and risks from components and degradation products of composite resin dental materials. Human and Ecological Risk Assessment, 3(4): 683-697. 1997
• A Monte Carlo Assessment of Mercury Exposure and Risks from Dental Amalgam. Human and Ecological Risk Assessment, vol. 2(no. 4): 709-761. 1996
– Assessment Of Mercury Exposure And Risks From Dental Amalgam. Health Canada, Bureau of Medical Devices. http://publications.gc.ca/collections/Collection/H46-1-36-1995E.pdf. 1995.
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